1. Field of the Invention
The present invention relates to a process for producing a colorant dispersoid in which a coloring material is dispersed with a block copolymer.
2. Related Background Art
Various aqueous dispersions containing a functional substance are well known: the functional substance including pesticides such as herbicides, and insecticides; medicines such as anticancer agents, antiallergic agents, and anti-inflammatory agents; and coloring matters for preparations such as inks and toners.
In recent years, digital printing techniques are developing rapidly. The digital techniques are typified by electrophotography techniques and inkjet techniques. The digital printing techniques are becoming more and more important in image formation in offices and homes.
Among the digital printing techniques, the inkjet printing techniques are characterized, as a direct recording method, by compactness of the apparatus, and low power consumption. The inkjet techniques are being improved rapidly in the image quality by making the nozzles finer. In an example of the inkjet techniques, ink supplied from an ink tank to a nozzle is heated by a heater in the nozzle and is allowed to evaporate and bubble to eject the ink from the nozzle to form an image on a recording medium. In another example of the inkjet techniques, the ink is ejected from the nozzle by vibration of a piezo element.
These inkjet methods usually use an aqueous dye solution as the ink. The aqueous ink tends to run on overlapping of the colors, or may cause feathering at the recording position on the recording medium along a paper fiber direction. To cancel such disadvantages, U.S. Pat. No. 5,085,698 discloses use of a pigment dispersion ink. This patent disclosure uses a pigment dispersion ink containing pigment particles stabilized by an AB-type or ABA-type block copolymer and an aqueous solvent. The pigment inks are produced in the working examples by use of a flask and a beaker.
U.S. Patent Publication No. 2002/040662A1 discloses a process for producing a pigment dispersion by collision of fluids ejected from nozzles in a reactor chamber. In this disclosed process, suspension liquids containing a crude pigment, a dispersion-stabilizing liquid, and a liquid medium are ejected through counterposed nozzles in the reactor chamber and brought into collision together to pulverize and disperse the crude pigment. However, this method needs further improvement for steady preparation of dispersion of finer-sized particles.
Microreactors are known as small-sized chemical devices of a three-dimensional structure utilizing a phenomenon in a microscopic space for reaction or mixing. The microreactor includes reactors and mixers having plural microscopic flow channels (hereinafter referred to as “a microchannel”, or “microchannels”). Examples are disclosed in literature such as “Microreactors New Technology for Modern Chemistry” (Wolfgang Ehrfeld, Volker Hassel, Holger Loewe; WILEY-VCH Co. 2000)
A process for producing effectively a solution of a metal colloid of a small particle size is disclosed in Japanese Patent Application Laid-Open No. 2004-33901. This patent document discloses a process for producing a metal colloid solution by reducing a metal compound in the presence of a polymeric dispersant for a pigment in a microreactor. The patent document describes effective production of a metal colloid of a small particle size, but discloses neither production of a colorant having a fine particle size nor use of a block copolymer as a dispersant for production thereof.
The present invention is made, on the aforementioned technical background, to provide a process for producing, by use of a microreactor, a colorant dispersoid of a small particle size comprising a coloring material and block copolymer.